When does riolu learn arua sphrere in Pokemon mystery dungeon exploreres of sky?

Riolu does not learn "Aura Sphere", as it is not in its learnset. To get Riolu to learn "Aura Sphere", you must evolve it into Lucario. Lucario learns Aura Sphere sometime in level 30-40. If you are higher than that, simply go to Electivire Link Shop